Dinoflagellate protozoan. Coloured scanning electron micrograph (SEM) of the test (encysted form) of a Gymnodinium lunula dinoflagellate. Dinoflagellates are unicellular protozoans. About 90% are found in marine environments as plankton. They range in size from 2 millimetres to less than a hundredth of a milimetre across. is one of the few naked dinoflagellates, or species lacking armor (cellulosic plates). Magnification: x40 when printed at 10 cemtimetres across.